1. Field of the Invention
This invention relates to a relay terminal interposed between an input-and-output unit of a programmable controller and a load to be controlled, and more particularly, to an improved relay terminal having a two step overlapping arrangement In which a relay group and terminal block are stacked vertically, thereby reducing an exclusive occupation area for installation on a control panel.
2. Description of the Related Art
Generally, if desired, a relay terminal is interposed between an input-and-output unit of a programmable controller and a load to be controlled. With such a construction that the load to be controlled is driven by employing such a relay terminal has tho advantages that the security of relay burnout is high, the degree of freedom about the selection of a power source is high, and the relay terminal may be arranged close to the load, in comparison with a direct drive system where the load to be controlled is directly driven by an input-and-output unit attached to a programmable controller.
Such a conventional relay terminal, however, employs a flat component construction in which a terminal block is mounted on a front area of a sheet of wiring board and a group of relays are mounted on a rear area of the board, and requires a large occupation area in a vertical direction when it is mounted on a vertical mounting wall within a control panel, thereby reducing the package density of the control panel.
It is, therefore, a primary object of this invention to provide a relay terminal capable of having a small occupation area on a mounting wall and increasing its package density.
According to the first aspect of this invention, there is provided a relay terminal including a plurality of relays, a connector for entering control signals to control the relays and outputting contact inputs from their relay contacts, and a terminal block corresponding to the input and output signals of the relays, which are held as a single unit, and the holding construction of the plurality of relays and the terminal block employs a two step overlapping holding construction in which the relays are hold in an upper step and the terminal block is held in a lower step. According to this relay terminal, the occupation width may be reduced in a vertical direction to improve the package density when the relay terminal is mounted on a vertical installation wall within a control panel.
According to the second aspect of this invention, there is provided a relay terminal according to the first aspect of this invention, further including an upper side holding member holding the plurality of relays and a lower side holding member holding the terminal block, in which a combination construction of the upper aide holding member and the lower side holding member is designed to be selectively set to a first condition in which the relays cover the upper of the terminal block or a second condition in which the relays do not cover the upper face of the terminal block. According to this relay terminal, the upper side holding member serves as a terminal block cover by taking the first condition on an electrically conductive condition, while screw work, when a wiring work of the terminal block is necessary, is eased by taking the second condition.
According to the third aspect of this invention, there is provided a relay terminal according to the second aspect of this invention, in which a terminal plate of the terminal block housed within the lower side holding member is extended to a connecting portion of the upper side holding member, the upper side holding member is inserted by a conductive member that is conductive with the terminal plate when the both holding member, are positioned to the first condition, and an end of the conductive member is exposed on an external wall of the holding member to provide a check terminal.
According to this relay terminal, when the upper and lower side holding members are positioned in the first condition, the check terminal is exposed on a surface of the upper side holding member, whereby operational confirmations or electrical checks may be easily performed by contacting a tester rod or the like to the check terminal.
According to the fourth aspect of this invention, there is provided a relay terminal according to the third aspect of this invention, in which the end of the terminal plate serves as a plug pin extending to the connecting portion of the upper side holding member, and the conductive member inserted. into the upper side holding member serves as a socket pin. According to this relay terminal, as the upper and lower side holding members are combined into the first condition, the plug pin and the socket pin are ensured to be conductive, thereby ensuring an electrical connection between the terminal or the terminal block and the check terminal.
According to the fifth aspect of this invention, there is provided a relay terminal according to one of the third and fourth aspects of this invention, in which a tip end of the check terminal is accommodated by a stepped concave hole disposed on a surface of the upper side holding member. This relay terminal prevents the check terminal from being carelessly contacted by a metal piece on the electrical conductors, whereby an unexpected accidental ground path may be avoided.
According to the sixth aspect of this invention, there is provided a relay terminal according to one of the second through fifth aspects of this invention, in which the combination construction is constructed so that relative positions of the both upper and lower side holding members are changeable between the first and second conditions. When the upper side holding member is mounted as a cover member for the lower side holding member for an open-and-close movement according to the construction of this relay terminal, the upper side holding member in the first condition may serve as a terminal cover for the lower side holding member, and the second condition allows the screw work of the terminal block to be eased.
According to the seventh aspect of this invention, there is provided a relay terminal according to one of the second through fifth aspects of this invention, in which the combination construction is a removable combination construction which is selectively set to one of the first and second conditions. When the upper side holding member is mounted as a removable cover member for the lower side holding member according to the construction of this relay terminal, the upper side holding member in the first condition may serve as a terminal cover for the lower side holding member, and the second condition allows the screwing work of the terminal block to be eased.
According to the eighth aspect of this invention, there is provided a relay terminal according to one of the second through fifth aspects of this invention, in which the lower side holding member is provided with a mounting space for an enlarged terminal block. This construction may omit any additional space for a terminal block beside the relay terminal to be connected with a load power source.